Calculate Your BMR: A Practical Guide to Smarter Weight Goals

If you’ve been cutting calories and still not seeing the results you expect, the missing piece may be your basal metabolic rate (BMR) — the energy your body uses just to stay alive. Understanding your BMR helps you set realistic calorie targets, avoid crash dieting, and tailor a plan that actually fits your life.

What is basal metabolic rate (BMR)?

BMR is the minimum number of calories your body needs at complete rest to power essential functions like breathing, circulation, temperature regulation, and cell repair. Think of it as your metabolism’s baseline — the largest slice of your daily energy “budget.”

• For most adults, BMR accounts for roughly 60–75% of total daily energy expenditure (TDEE)
• The rest comes from movement (exercise and non-exercise activity) and the thermic effect of food (the energy used to digest and process what you eat)

BMR vs RMR (and why it matters)

• BMR is measured under strict lab conditions (fasted, thermoneutral environment, complete rest).
• Resting metabolic rate (RMR) is similar but measured under less strict conditions and is typically a bit higher than BMR.
• Most consumer calculators labeled “BMR” actually estimate RMR. That’s okay — use the number as your baseline and adjust with real-world data.

What influences your BMR

• Body size and lean mass: More muscle generally means a higher BMR.
• Sex and age: BMR tends to be higher in men and declines with age.
• Genetics and hormones: Thyroid function, menstrual cycle phase, and other hormones influence energy use.
• Medications and health conditions: Steroids, beta-blockers, thyroid disorders, and others can shift metabolism.

How to calculate BMR (with examples)

Several validated equations estimate BMR/RMR using your age, sex, height, and weight. Here are the most useful options.

1) Mifflin–St Jeor (recommended for most adults)

• Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
• Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161

This equation is widely considered the most accurate for the general population and is the default for many dietitians and clinicians.

2) Revised Harris–Benedict

• Men: BMR = 13.397 × weight(kg) + 4.799 × height(cm) − 5.677 × age + 88.362
• Women: BMR = 9.247 × weight(kg) + 3.098 × height(cm) − 4.330 × age + 447.593

Useful, but can slightly overestimate for some people compared to Mifflin–St Jeor.

3) Katch–McArdle (best if you know your body fat %)

• BMR = 370 + 21.6 × LBM(kg), where LBM = lean body mass
• LBM(kg) = weight(kg) × (1 − body fat %)

Great for those with reliable body-composition data (e.g., DEXA).

Quick examples

• Woman, 35 years, 70 kg, 165 cm (Mifflin–St Jeor):
  • 10×70 + 6.25×165 − 5×35 − 161 = 700 + 1031.25 − 175 − 161 ≈ 1,395 kcal/day
• Man, 35 years, 85 kg, 180 cm (Mifflin–St Jeor):
  • 10×85 + 6.25×180 − 5×35 + 5 = 850 + 1125 − 175 + 5 ≈ 1,805 kcal/day

Common calculation pitfalls to avoid

• Mixing units (lbs vs kg; inches vs cm). Convert first: kg = lbs ÷ 2.205; cm = inches × 2.54.
• Overestimating activity level (most of us are more sedentary than we think).
• Treating an estimate as a fixed truth. Your metabolism isn’t a single, unchanging number.

From BMR to daily calories: estimating TDEE

To estimate your total daily energy expenditure (TDEE), multiply your BMR by an activity factor:

• Sedentary (desk job, minimal exercise): × 1.2
• Lightly active (1–3 exercise days/week or 5,000–7,000 steps): × 1.375
• Moderately active (3–5 exercise days/week or 7,000–10,000 steps): × 1.55
• Very active (6–7 exercise days/week, physical job, 10,000–14,000 steps): × 1.725
• Extra active (manual labor + training, >14,000 steps): × 1.9

Tip: If you’re between categories, pick the lower one to start. You can always adjust.

Setting calorie targets for your goals

• Fat loss: Aim for a 10–20% calorie deficit from TDEE (roughly 300–500 kcal/day for many). Target 0.5–1.0% body weight loss per week.
• Maintenance: Eat around your TDEE. Expect small day-to-day weight swings from water and glycogen.
• Muscle gain: 5–10% calorie surplus, paired with progressive strength training. Weight gain of ~0.25–0.5% per week helps limit fat gain.

Macronutrients that help:

• Protein: 1.2–1.6 g per kg body weight (up to ~2.2 g/kg if training hard) supports muscle retention during fat loss.
• Fiber: 25–35 g/day from plants to support fullness, gut health, and overall diet quality.

Worked example: from BMR to a fat-loss target

Using the 35-year-old woman example above (BMR ≈ 1,395 kcal) and lightly active (×1.375):

• TDEE ≈ 1,395 × 1.375 ≈ 1,918 kcal/day
• A 15% deficit: 1,918 × 0.85 ≈ 1,630 kcal/day
• Protein target: 1.4 g/kg × 70 kg ≈ ~100 g protein/day

Calibrate with real-world data (the 2-week check)

Your body is the best “calculator.”

1. Follow your target for 14 days.
2. Track average daily calories and your scale trend (weigh 3–4 mornings/week and average).
3. If weight isn’t moving as expected, adjust by 100–150 kcal and reassess for another 1–2 weeks.

Can you change your BMR?

You can’t rewrite your genetics, but you can influence BMR over time.

• Build and keep muscle: 2–4 days/week of resistance training preserves or increases lean mass, nudging BMR upward.
• Prioritise protein: 1.2–1.6 g/kg/day helps protect muscle during a deficit and slightly increases the thermic effect of food.
• Move more between workouts (NEAT): Walk breaks, standing more, taking stairs — these mini-movements add up meaningfully to daily burn.
• Sleep 7–9 hours: Short sleep is linked to poorer appetite regulation and lower daily energy expenditure.
• Manage stress: High stress can reduce NEAT and increase cravings.
• Medical check-ups: If weight changes are unexpected, ask your clinician about thyroid function, medications, and other conditions that affect metabolism.
• Small, short-term boosts: Caffeine can slightly increase energy expenditure; cold exposure may have modest effects. “Detoxes” and fat-burning supplements are not evidence-based solutions.

What is a “healthy” BMR for my age and lifestyle?

There isn’t a single “good” BMR. It’s normal for BMR to vary by sex, age, height, and muscle mass. BMR tends to decline gradually with age, largely due to changes in body composition. Rather than chasing a target number, use your BMR as a personalised starting point to set calories, then let your progress guide adjustments.

Quick answers to common questions

• My BMR seems low. Does that mean I can’t lose weight? No. It simply means your calorie needs are lower. You can still lose weight with a modest, sustainable deficit and a focus on protein and strength training.
• Should I never eat below my BMR? That’s a myth. On some days you may eat below BMR, especially during fat loss. What matters is overall nutrition, sustainability, and health. Very low-calorie diets should be medically supervised.
• Are wearables accurate for calories burned? They’re useful for step counts and trends, but calorie estimates can be off. Use them to support habits, not as absolute truth.
• Does my menstrual cycle affect energy needs? Yes, many people experience a small increase in energy expenditure and appetite in the late luteal phase. Plan for a bit more hunger and focus on protein and fiber.
• Do I need to recalculate as I lose weight? Reassess every 4–6 weeks or after ~5% body weight change. As you lose weight, your energy needs will drop slightly.

Practical checklist: set your calorie target today

1. Choose a formula (Mifflin–St Jeor is a solid default) and calculate your BMR.
2. Pick an activity factor based on your weekly steps and training.
3. Compute your TDEE (BMR × activity factor).
4. Set a goal-based adjustment (deficit or surplus) of 10–20%.
5. Hit a protein target of 1.2–1.6 g/kg and aim for 25–35 g fiber/day.
6. Track for 2 weeks, then adjust by 100–150 kcal if needed.

Key takeaways

• BMR is your metabolic baseline and the foundation for calorie targets.
• Use BMR to estimate TDEE, then tailor intake for fat loss, maintenance, or muscle gain.
• The best plan is personalised: start with a good estimate and fine-tune using your progress.
• Resistance training, sufficient protein, quality sleep, and daily movement help protect or gently raise your metabolic baseline.

If you want personalised guidance that adapts to your lifestyle and goals, HeySlim can help you turn these numbers into a simple, sustainable plan.

References

• Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990. https://pubmed.ncbi.nlm.nih.gov/2305711/
• Harris JA, Benedict FG. A biometric study of basal metabolism in man. 1919. (Revised equations commonly used.) https://pmc.ncbi.nlm.nih.gov/articles/PMC1091498/
• Cleveland Clinic. Basal Metabolic Rate (BMR). https://my.clevelandclinic.org/health/body/basal-metabolic-rate-bmr
• FAO/WHO/UNU Expert Consultation. Human energy requirements. 2004. https://www.fao.org/3/y5686e/y5686e.pdf
• Hall KD et al. Energy balance and its components: implications for body weight regulation. Am J Clin Nutr. 2012. https://pubmed.ncbi.nlm.nih.gov/22434603/
• International Society of Sports Nutrition Position Stand: Protein and exercise. JISSN. 2017. https://jissn.biomedcentral.com/articles/10.1186/s12970-017-0177-8

Note: This article is educational and not a substitute for personalised medical advice. If you’re pregnant, breastfeeding, managing a medical condition, or taking medications that affect appetite or metabolism, consult your healthcare provider before making significant diet changes.